Synchronous Digital Hierarchy (SDH) is a CCITT standard for a hierarchy of optical transmission rates. Synchronous Optical Network (SONET) is a USA standard that is largely equivalent to SDH. Both are widely used methods for very high speed transmission of voice and data signals across the numerous world-wide fiber-optic networks.
SDH and SONET use light-emitting diodes or lasers to transmit a binary stream of light-on and light-off sequences at a constant rate. At the far end optical sensors convert the pulses of light back to electrical representations of the binary information.
The basic building block of the SONET/SDH hierarchy in the optical domain is an OC1; in the electrical domain, it is an STS-1. An OC1 operates at 51.840 Mbps. OC3 operates at 155.520 Mbps.
Optical Transport Network (OTN) technology represents both a technical leap forward in optical networking over SONET/SDH and a business opportunity for carriers and service providers alike.
|Asynchronous mapping of payloads||Synchronous mapping of payloads|
|Timing distribution not required||Requires right timing distribution across networks|
|Designed to operate on multiple wavelengths||Designed to operate on multiple wavelengths|
|Scales to 100Gb/s (and beyond)||Scales to a maximum of 40 Gb/s|
|Performs single-stage multiplexing||Performs multi-stage multiplexing|
|Uses a fixed frame size and increases frame rate to match client rates||Uses a fixed frame rate for a given line rate and increases frame size as client size increases|
|FEC sized for error correction to correct 16 blocks per frame||Not applicable (no standardized FEC)|